Power analysis of system-level on-chip communication architectures

For complex system-on-chips (SoCs) fabricated in nanometer technologies, the system-level on-chip communication architecture is emerging as a significant source of power consumption. Managing and optimizing this important component of SoC power requires a detailed understanding of the characteristics of its power consumption. Various power estimation and low-power design techniques have been proposed for the global interconnects that form part of SoC communication architectures (e.g., low-swing buses, bus encoding, etc). While effective, they only address a limited part of communication architecture power consumption. A state-of-the-art communication architecture, viewed in its entirety, is quite complex, comprising several components, such as bus interfaces, arbiters, bridges, decoders, and multiplexers, in addition to the global bus lines. Relatively little research has focused on analyzing and comparing the power consumed by different components of the communication architecture. In this work, we present a systematic evaluation and analysis of the power consumed by a state-of-the-art communication architecture (the AMBA on-chip bus), using a commercial design flow. We focus on developing a quantitative understanding of the relative contributions of different communication architecture components to its power consumption, and the factors on which they depend. We decompose the communication architecture power into power consumed by logic components (such as arbiters, decoders, bus bridges), global bus lines (that carry address, data, and control information), and bus interfaces. We also perform studies that analyze the impact of varying application traffic characteristics, and varying SoC complexity, on communication architecture power. Based on our analyses, we evaluate different techniques for reducing the power consumed by the on-chip communication architecture, and compare their effectiveness in achieving power savings at the system level. In addition to quantitatively reinforcing the view that on-chip communication is an important target for system-level power optimization, our work demonstrates (i) the importance of considering the communication architecture in its entirety, and (ii) the opportunities that exist for power reduction through careful communication architecture design.